The present invention relates generally to blast stoves and in particular to a structure for supporting checkerbrick within the stove.
Blast stoves are employed in iron making processes to preheat the combustion air before entry into a blast furnace. Typically, a blast stove is a silo shaped structure constructed or refractory and insulating brick and surrounded by a metallic shell. Adjoining combustion and regenerative chambers are enclosed within the structure and communicate through a passage formed by a domed top.
The regenerative or checker chamber includes tiers of refractory brick which fill a major portion of the chamber volume. This checkerbrick generally includes aligned flow passages which extend from the top to the bottom of the checkerwork.
A blast stove has two cycles of operation--a heating cycle and a blast cycle. During the heating cycle, combustible gases generated during iron making by an associated blast furnace are introduced into the combustion chamber through a valve controlled port along with an appropriate amount of combustion air at the bottom of the chamber and then burned. The burning gases travel upwardly to the top of the stove, then down through the checkerwork, and finally out through a valve control port at the bottom of the checker chamber. The heat of combustion of the burning gases is absorbed by the checkerbrick and once the checker-work reaches a predetermined temperature, the heating cycle is terminated and the blast cycle is initiated. In the blast cycle, air is introduced at the base of the checker chamber, is heated as it travels through the checkerbrick and then is conveyed from the combustion chamber to the blast furnace.
The repetitive thermal cycling of the blast stove, subjects the structure to substantial thermal related stresses. The stress induced movement in various structural components, if not controlled, may precipitate catastrophic, fatigue and creep related failures in the blast stove. This movement is gradual and results from the thermal cycling. In theory, each component will, during a thermal cycle, expand and then contract to its original position. In practice, frictional engagement between a member and its supports is often not uniform and as a consequence the member will move slightly during each thermal cycle. With prior structures, such member movement accumulated over repetitive thermal cycles.
Because of this accumulated movement, it was not uncommon, for example, to find after a few years of use, that portions of the checkerwork support structure have moved beyond permissible limits. As a result, the checkerbrick is no longer uniformly supported and the structure may become dangerously unstable.
An even more common occurrence is one in which the accumulated structure and checkerbrick movement is random, causing a misalignment of the flow passages in the checkerbrick. This misalignment will substantially restrict flow through the checker-work. Because the efficiency of the blast stove is directly related to the rate of air flow it is able to sustain, once the checkerbrick becomes excessively misaligned, the blast stove is rendered substantially useless.
Prior art structures have been suggested to deal with thermal induced structural movements, but none have proved totally effective. One such attempt has suggested the placement of a layer of metallic "shoes" on a grid supported by parallel girders. The "shoes" are configured to engage the first layer of checkerbrick layed upon it. The configuration, however, allows the uncontrolled movement between the metal shoe engaged by the brick and the grid work which supports the layer of metal shoes. Moreover, the checkerwork is not constrained from moving into or against the interior wall of the blast stove.
A second suggested structure would use a "filler brick" in some of the flow passages of the bottom layer of checkerbrick to extend down into the grid work supporting the first layer of checkerbrick, to interlock the checkerbrick to the grid work. It would appear that in this structure, the flow passages through the checkerbrick would be obstructed by the required filler brick.
Still another suggested supporting structure would use a layer of metallic shoes, each having a downwardly extending lug to engage a supporting, parallel grid work below the layer. This configuration would limit the lateral movement of the grid shoe with respect to the grid in one direction only.
Finally, a more recent proposal would utilize a labyrinth of girders and grid bars for supporting the checkerwork. To maintain the spatial distances between the members, spacers and pivotal connections are employed at various locations. This construction is unduly complex and possibly does not allow sufficient movement in response to the thermal stresses, that are experienced in use.